Clinical use of endoscopic devices and probes has permitted physicians to view and diagnose target bodies, such as tumors, deposits, tears, thrombi, and the like. Unfortunately, there are still a number of disadvantages and limitations of using conventionally available endoscopes. The diameter of currently available probes limits their use to certain procedures and locations that can accommodate the large diameter of the endoscope. Consequently, many procedures currently done surgically could be done endoscopically, if a small enough probe was available with a sufficient number of resolvable points.
Current endoscopic procedures generally require administration of anesthesia and surgical training for insertion. Certain procedures cannot currently be done endoscopically because of the diameter of existing probes. Probe size is proportional to the likelihood of tissue damage occurring during the procedure. Another problem associated with current probes is the occurrence of adverse reactions, such as in fetoscopy, where the risk to the fetus is high. Neural imaging carries with it the possibility of brain damage. Spinal canal and brain ventricular imaging have complications of spinal fluid leakage and headaches which are more frequent and severe with larger diameter probes. Catheterization of the pancreatic duct is also problematic due to the probe size and resultant complications which include acute pancreatitis. Also, the size of the incision necessary to insert current probes results in longer healing time and more prominent scarring.
Present day miniature endoscopes are composed of fiber-optic imaging bundles. Currently, the clinical use of small diameter endoscopes is limited by poor resolution. Available miniature endoscopes have diameters in the range of from about 0.35 mm to about 1.0 mm. Since optical fibers are of finite diameter, only a limited number of fibers can be incorporated into one imaging bundle, resulting in a limited number of resolvable elements. For example, for a 1 mm fiber optic imaging bundle with an individual fiber diameter of 10 μm, the total number of resolvable points is 9000 with 100 resolvable points across the field of view. In addition, the fill factor is about 85% resulting dead space from the cladding material and causing the image to have a pixelated or “honeycomb” appearance. These two technical problems have severely limited the clinical use of currently available sub-millimeter diameter imaging probes. In order to achieve a higher number of resolvable elements with such probes, larger diameters must be used, which obviate their use in smaller spaces and eliminate certain procedures from being done endoscopically. If one uses a currently available probe in the sub-millimeter diameter range, the number of resolvable points obtainable drops below clinically useful levels. Present endoscopes have a light transmission efficiency of up to about 50%.
A further disadvantage of fiber bundles is that crosstalk occurs, reducing the signal to noise level. Moreover, as fiber length increases, light transmission efficiency decreases. Also with current fiber optic endoscopes, coupling illumination light into the fiber optic imaging bundle is difficult. As a result, miniature endoscopes need two separate fiber bundles, one for illumination and one for detection of the image. The need for distinct illumination and detection bundles increases (at least doubles) the overall endoscope diameter. It would therefore be desirable to have a long length endoscope probe that retains sufficient light transmission efficiency to provide a clinically useful image and information.
Another disadvantage of optical fiber bundles is that individual fibers may be broken or have defects at their faces, resulting in “dead” pixels. The use of one fiber would greatly minimize the presence of dead pixels.
Thus, it would be desirable to have a probe that provided a satisfactory number of resolvable elements in a space/diameter below a certain size that would enable procedures to be done currently not achievable by currently available endoscopes. It would be desirable to have a probe in the sub-millimeter diameter range that had optics that would improve the number of resolvable points, reduce deadspace/fill factor, and minimize risk of adverse consequences to the patient. Such a novel probe would enable procedures to be performable that currently cannot be attempted endoscopically, such as, but not limited to, otological, neural, pancreatic, and fetal surgical endoscopy. It would also be desirable to have a sub-millimeter endoscope that would allow for diagnosis as well as treatment in a single device.
Spectral encoding is a method that allows detection of a one-dimensional line of an image using a single optical fiber. Encoding the spatial information on the sample is accomplished by using a broad bandwidth source as the input to the endoscope. The source spectrum is dispersed by a grating and focused by a lens onto the sample. The spot for each wavelength is then focused at a separate position, x, on the sample. The reflectance as a function of transverse location is determined by measuring the reflected spectrum. The other dimension of the image can be obtained by mechanical scanning at a slower rate. The advantage of this mode of imaging is that the fast scanning needed to produce an image at or near video frame rates is performed externally to the probe, making the construction of small diameter probes feasible.